How was steel made in the Middle Ages? A step-by-step guide!

Medieval myths and tales often connect the forging of swords with dwarves and other magical creatures. And indeed, the process of transforming a piece of Iron into a steel sword that could cut extremely well must have seemed like a magical procedure to medieval people.

Especially because the entire procedure took place in a gloomy forge (a gloomy forge was important so that the blacksmith could closely watch the iron and its different colors to evaluate its temperature) which made the entire journey from a piece of iron to a steel sword even more mystical.

So in the following, I would like to pull back the curtain of the darkened forges and present how steel was made in the Middle Ages.

Iron had to be carburized to turn into steel. To archive that, iron was mixed with charcoal, the charcoal was brought to a glow, and as a result, carbon atoms from the charcoal diffused into the surface of the iron. To achieve an even better steel bird droppings that were high in carbon and nitrogen were added. The steel could then be forged into weapons.

Let`s find out more by starting with the difference between Iron and Steel.

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Who was the first to use steel?

While most of the weapons that were used in Antiquity were made from bronze or iron the Romans also used steel swords made from „Ferrum Noricum“, the Noric steel. These swords that were made from Noric steel were so good that the Romans prohibited the export of these weapons into territories outside of the Roman Empire, basically the world’s first weapons embargo.

By the way, Noric steel got its name from the Roman province of Noricum (today parts of Bavaria, Austria, and Slovenia) where the iron ore was mined. The reason for the edge retention, the cutting abilities, and the sharpening ability of swords made from Noric steel can be found in the composition of the used iron ore that had a high proportion of manganese and a low proportion of phosphorus.

Because of these good qualities, all the Ferrum Noricum that was mined since the Province of Noricum had been added to the Roman territory in 16 BC was claimed by the Roman military. By the way. While steel was already known in Antiquity there was no word for that material. So the Romans called the material that we know as steel „good iron“ or, in the case of the Noric steel „Ferrum (=Iron) Noricum).

However, the secrets of the production of steel had already been discovered long before the Romans ever built their Empire, here you can find out more about the Roman expansion.

The Hittites had already discovered the secrets of producing steel around the year 1,500 BC but had guarded these secrets as a state secret. During that time steel weapons were precious gifts since they were superior to the widely used bronze or iron weapons. Only after the fall of the Hittite Empire did the secrets of how to make steel slowly spread over the Near East and later the world.

The big advantage that steel weapons offered compared to their bronze and iron counterparts was that they were much harder. Unlike iron, steel can be hardened. But to be able to harden steel the material needed a minimum of 0,35% of carbon content. And a steel sword of average quality needed at least a content of 0,5% carbon.

So now we have established some facts.

But how was steel now made during the Middle Ages? Let`s start out by looking at how the basic material, iron, was extracted during the Middle Ages.

The production of Iron in the Middle Ages

First of all, it is important to state that medieval iron didn`t have a lot to do with modern-day cast iron. Modern-day cast iron is pretty brittle and has a carbon content of more than 2% while medieval iron was rather soft and had a low carbon content.

Until the High Middle Ages, iron was extracted by using a bloomery. Originally pits at the side of mountains were used for that so that the breeze was fanning the flames and temperatures that were high enough were reached. Later that job was done by bellows. These bloomers were preheated by burning charcoal in them, then a 1-on-1 mixture of iron ore and charcoal was added. Small particles of Iron would drop down, combine with molten slag, and form a highly porous mass when cooling down.

Then the mass of iron and slag had to be repeatedly heated and worked with a hammer until most of the slag had been massaged out and only the iron was left. That iron was then sold in the shape of bars from which steel could then be made.

How was steel made in the Middle Ages?

But these bars of iron were not usable to forge a steel sword from them since iron in the Middle Ages usually only had a low carbon content while an average quality steel sword needed a carbon content of at least 0,5%.

So the iron bars had to be turned into steel.

And that was done by carburizing them. Carburizing means that iron and charcoal were mixed together and brought to a glow so that the carbon molecules diffused into the iron. Some blacksmiths also added bird droppings to make the steel even harder, but the reasoning behind that will be explained under the next headline.

Carburizing the iron bars took a lot of time, a total of 12 hours, and a constant temperature of 900° Celsius (= 1652° Fahrenheit) of carburization was necessary to achieve a 2 millimeters deep surface carburization of the iron bar.

And even when the bars were successfully carburized they still had to be forged out several times until a blade could be forged. Later that blade was then sharpened which was also a long process, more on how swords were sharpened for the first time and how knights kept their swords sharp in my article here.

However, sometimes adding charcoal for carburization was not seen as sufficient to create the best steel possible. Sometimes other, more surprising materials were used instead.

Adding bird droppings to the carburization process to produce an even harder steel

Now you might have cringed when reading that headline. Who in his right mind would add bird droppings when making steel?

Bird droppings contain not only a high amount of carbon but also nitrogen which also diffuses into the iron during the carburization process. The additional nitrogen molecules create a steel that is much harder than steel that is just carburized with charcoal.

That process of using bird dropping to produce extremely hard steel can be found in both medieval legends like the saga of Wayland the Smith that you can find here* on Amazon.

But not only do legends mention the use of bird droppings during the making of steel. The Arabian scholar al-Biruni who lived from 973 to 1053 mentioned that the steel that was used for the swords of the Rus was made by carburizing the iron by adding bird droppings.

By the way. The benefits of adding nitrogen compounds were also used for tempering swords when they were quenched in blood rather than in water or oil.

Yes, you read correctly. Sources are indicating that some swords were quenched in blood and there is scientific evidence why that was beneficial. You can find out more about that (and why quenching a sword in urine instead of blood was even better. Well, at least in theory) in my article here.

Take care of yourself because you deserve it. You really do.

Until next time

Yours truly

Luke Reitzer


Thomas Laible: Das Schwert. Mythos und Wirklichkeit (Bad Aibling 2008).